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  1. KrisBlueNZ

    what exactly is Voltage

    Good answer Laplace. I read the linked descriptions that try to explain what voltage is. I didn't find them meaningful; maybe that's because I've never been strong on physics. I like your analogy to gravity. Everyone knows what gravity is... until we're asked to actually explain it. All we can...
  2. KrisBlueNZ

    Need help to fix motion detector alarm

    The LED doesn't turn off? I'd expect that's the first problem. The alarm isn't armed until the LED turns off, so if that doesn't happen, the alarm will never activate. I guess it's possible that a faulty sensor could be preventing the circuit from arming. Make sure you hold the board vertical...
  3. KrisBlueNZ

    Rewiring 7-band EQ

    That looks good at first glance. Nice work! It's very unlikely you'll start a fire with it; it's not even likely you'll do any damage to anything even if there's an error. But you can start with the IC unplugged and make some measurements on the IC socket. With the power conected and your...
  4. KrisBlueNZ

    Power loss and Energy loss

    Power (watts) is a measure of the rate of energy flow. When you turn on a 60W light bulb, it converts energy from electrical energy to light and heat at a rate of 60 joules per second. Every second that the light bulb is turned on, 60 joules of energy is converted from one form to the other. So...
  5. KrisBlueNZ

    what exactly is Voltage

    What? None of those statements is true. Especially the last one. As for what voltage is, I can't actually explain it, although I've been an electronics engineer for 20+ years. Voltage used to be called "electromotive force" (EMF), i.e. a force that makes electrons move, and that's true in that...
  6. KrisBlueNZ

    Negative Voltage on Breadboard with no negative voltage input

    Or if there's no significant current into the ground rail, you don't even need the op-amp. The op-amp is a good idea if you're already using three op-amps from a quad package.
  7. KrisBlueNZ

    Sony TA-AX235 Protection

    Why don't you tell us what else you already did?
  8. KrisBlueNZ

    Need help to build police siren/LED flasher

    Q1~4 are transistors, not capacitors. Q1~3 are NPNs, type 2SC1815 or 2SC945, and Q4 is PNP, type 2SA1015. (The "2S" prefixes are often omitted.) At first glance, it looks like you've got the components right, but all those leads underneath are bound to be shorting onto each other, and onto...
  9. KrisBlueNZ

    Valve actuator project

    So you need to supply continuous 24V (DC I assume?) between either wires X and Y, or between wires Z and Y, depending on the time of day? There are lots of "proper" ways to do this, but for something that's quick to set up, you can use a permanently running 24V power supply feeding through...
  10. KrisBlueNZ

    Sony TA-AX235 Protection

    I would be carefully inspecting the solder connections on the pins of the output IC. It's easy to fracture the solder connections when you're screwing the IC onto the heatsink. Especially if it's a single-sided board. If in doubt, resolder them all - suck the old solder off first and don't use...
  11. KrisBlueNZ

    H-Bridge Circuit Design

    Right, thanks. That looks like a reasonable solution. You'll need to change the 100k resistor from the 555's ground rail to the 0V rail. They say that 100k was chosen for a 500V +HV rail. It would have about 485V across it, so 100k will give a current of 4.85 mA. That seems reasonable provided...
  12. KrisBlueNZ

    Discharging battery

    Are you sure the solar panel is large enough? It needs to provide enough average current to cover the average load on the battery, plus a bit because the battery isn't 100% efficient, plus a bit for the leakage current of the battery, when averaged over a period of a few days. Even during...
  13. KrisBlueNZ

    Negative Voltage on Breadboard with no negative voltage input

    The ICL7660 is the old standard for generating a negative supply rail from a positive supply. It uses a switched capacitor arrangement and it can't supply much current but this is usually OK for op-amp circuits. There are other similar devices such as LT1054 and MAX1044. These are good if you...
  14. KrisBlueNZ

    H-Bridge Circuit Design

    I've never actually used H-bridge driver ICs myself! I just understand how they work. Of the three you listed, the IR2184 is the only one that has the important features - high-side and low-side drive and dead time enforcement. It looks pretty good to me. Can you point me to any application...
  15. KrisBlueNZ

    H-Bridge Circuit Design

    Whoa! Fish, thanks for your explanation of your dyslexia! It sounds like nothing I can imagine. I don't have any problem with letters, or left/right. Sometimes I'll get doubled-up numbers wrong - like I might write 3360 when it should be 3660 or something like that. But full-on dyslexia must be...
  16. KrisBlueNZ

    Need help to fix motion detector alarm

    I think it's fairly likely that the sensor is a normally open switch that makes contact when moved. Turn it on, wait for the LED to go out, and try connecting the two clips together, using a pair of pliers or something. If that sets off the alarm, the rest of the circuit is working. Can you...
  17. KrisBlueNZ

    Power supply lost -5 volts

    It's a diode. The third one from the left. LOL What kind of power supply is it? Can you post some photos of the main circuit board?
  18. KrisBlueNZ

    HDTV Melted Wires

    Um... can you post some photos? Use the Go Advanced button and click the paper clip icon. Maximum JPEG file size is about 150k I think, so you may need to rescale the pics first.
  19. KrisBlueNZ

    LED Flasher help.

    I just discovered an error in the schematic (I was trying to be clever, and failed) and made some wanted changes. Here's the updated schematic.
  20. KrisBlueNZ

    LED Flasher help.

    Thanks Bob :-) That's a really good idea. It would be a good example to contrast discrete design against microcontroller-based design. Hardware-wise, a microcontroller-based solution would be very simple - apart from the pushbutton and the LEDs, I think all you'd need would be a 14-pin PIC...
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